Researchers at ISTC find new way to enhance SAFs with waste plastic
Research Scientist Hong Lu has developed a way to convert polystyrene plastics into an additive to jet fuel that could help advance the effort to producing sustainably produced jet fuels. The process involves heat and pressure, as well as adding hydrogen, eventually separating out the liquid shown in the photo. Currently, this type of polystyrene plastic, largely used in food containers, is not saved for recycling. If the process scales to industrial use, it could keep this type of plastic out of landfills.Photo taken at the University of Illinois Urbana-Champaign on Thursday, Dec. 19, 2024. (Photo by Fred Zwicky / University of Illinois Urbana-Champaign)
Researchers at the Illinois Sustainable Technology Center (ISTC) launched a new study reporting a cost-effective method for producing ethylbenzene — an additive that improves the functional characteristics of sustainable aviation fuels — from consumer-grade hard plastic polystyrene.
Fuels derived from waste fat, oil, grease, plant biomass or other non-petroleum sources lack sufficient levels of aromatic hydrocarbons, which help keep fuel systems operational by lubricating mechanical parts and swelling the seals that protect from leaks during normal operations, said Hong Lu, a research scientist at the Illinois Sustainable Technology Center who led the new research.
The researchers used thermal pyrolysis to convert polystyrene to ethylbenzene, heating it to break the polymer down into a styrene-rich liquid. A second step, hydrogenation, converted it into a crude ethylbenzene, and distillation yielded a product that was 90% pure.
When mixed with a SAF, the polystyrene-derived ethylbenzene performed “almost as well as ethylbenzene derived from fossil fuels,” Lu said. The researchers said that a further purification would improve its performance.
The findings are reported in the journal ACS Sustainable Chemistry and Engineering.
Research highlighted that present standards require a minimum of 8.4% aromatic hydrocarbons be included in any blend of SAFs and fossil-derived fuels “to maintain compatibility with existing aircraft and related infrastructure.” While this rule increases the safety and efficacy of the overall fuel mix, it severely limits the use of sustainable fuels, which currently contain only about 0.5% aromatic hydrocarbons, Lu said.
“Currently, they use a blend of 20% to 30% SAFs and 70% to 80% conventional jet fuel,” he said.
This lag in conversion to sustainable fuels stems from several factors, one of which is the need for enough aromatic hydrocarbons in the mix. Other important factors involve qualities like the blend’s volatility, acidity, moisture content and freeze point.
“We did a preliminary cost analysis, and we found that the ethylbenzene produced from waste polystyrene is cheaper than that produced from crude oil. And a lifecycle analysis of our ethylbenzene found it reduced carbon emissions by 50% to 60% compared with the ethylbenzene made from crude oil,” Lu added further.
Lu and his colleagues hope to further develop this additive to help expand the use of SAFs in aviation.
Earlier in September last year, the researchers revealed that waste plastic can be transformed into a SAF. At the time, the team of researchers led by Lu successfully depolymerized polystyrene plastic to create a crude oil that can be blended with traditional aviation fuel to improve its performance.
ISTC is a division of the Prairie Research Institute at the University of Illinois Urbana-Champaign.